Differential Effects of Epidermal Growth Factor and Transforming

Differentiation of pulmonary Type I1 epithelial cells in late gestation is associated with the synthesis of pulmonary surfactant required for adaptation to air breathing at birth. In the present work, induction of synthesis of a Type I1 epithelial cell protein, surfactant-associated glycoprotein of M, = 35,000 (SAP-35) was studied in human fetal lung tissue obtained at 1524 weeks of gestation. SAP-35 content increased during organ culture in the absence of exogenous hormones. Epidermal growth factor or triiodothyronine stimulated the induction of SAP-35 synthesis during culture. Stimulation by epidermal growth factor (EGF) was detected as early as 2 days and persisted for up to 5 days in culture. Response to EGF was dose-dependent (0.01-10 ng/ml) and was associated with enhanced incorporation of [3SS]methionine into immunoprecipitable SAP-35. Increased SAP-35 synthesis was associated with increased SAP-35 RNA as assessed by Northern blot and hybridization assays with human SAP-35 cDNA. Effects of EGF were comparable to the induction of SAP-35 synthesis by 8-bromo-CAMP. In contrast to the stimulatory effect of EGF and triiodothyronine, SAP-35 content was inhibited by transforming growth factor-& Both the stimulatory and inhibitory effects of these agents on SAP-35 content were associated with concomitant changes in SAP-35 synthesis. These findings demonstrate multihormonal control of SAP-35 expression and strongly implicate both EGF and transforming growth factor-8 in the regulation of surfactant apoprotein synthesis.